The invention pertains to a pressure transducer and, in particular, to a pressure transducer for invasive blood pressure measurements.
A pressure transducer of this type is known from European Patent No. 0,360,286A2. In this case, a pressure measuring element is fastened onto a flat substrate. Electric conductors arranged on the substrate extend laterally to contact points arranged on the edge of the substrate. An electric cable is soldered onto these contact points.
French Patent No. 2,125,991 describes a similar pressure transducer with a housing that is divided into two separate chambers in a fluid-proof fashion via a membrane, whereby the first chamber is connected to an inlet opening and an outlet opening for the fluid. The second chamber contains a pressure measuring element that converts the fluid pressure that is applied to the said pressure measuring element via the membrane into electronic signals. These signals are transmitted from the second chamber toward the outside via electric conductors.
These devices are reusable pressure transducers with a so-called pressure dome that may be unscrewed, cleaned and sterilized after being used such that they may be reused. Due to the high expenditures associated with the cleaning and sterilization process, disposable pressure transducers primarily have been used for medical purposes since the beginning of the 1990's. These disposable pressure transducers are easier to handle with respect to their operation, maintenance, etc., and significantly reduce the risk of infection for the patient. In these instances, miniaturized pressure measuring elements are used that are fastened onto a ceramic substrate which, in the form of a printed circuit, also contains the external wiring of the pressure measuring element or balancing resistors, etc., and printed conductors. A pressure measuring element of this type is disclosed in U.S. Pat. No. 4,023,562.
Pressure measuring elements of this type in principle are designed in the form of a Wheatstone bridge circuit with a resistive wire strain gauge or another transducer that converts a pressure or a mechanical load into electronic signals, e.g., transducers known from German Patent (OLS) No. 2,916,390.
The first pressure transducer that is used for blood pressure measurements and operates with such pressure measuring elements is described in the company prospectus "Disposable Transducers" that was published by the firm Cobe Laboratories Inc. in 1983. In this pressure transducer, the ceramic substrate with the pressure measuring element was inserted into a pressure measuring chamber that was closed in a fluid-proof fashion and connected to an inlet opening and an outlet opening for the fluid. The electric connections for ascertaining the measured values extended laterally from this chamber in the form of printed conductors and were rigidly soldered at this location onto a cable connected to the housing of the pressure transducer.
German Patent No. 2,946,515 A1 discloses a pressure transducer with Hall IC in which the electric conductors of the pressure measuring element extend to plug-in contacts that are rigidly arranged in the housing. These plug-in contacts produce the electric connection with a cable via a plug/socket connection.
One additional pressure transducer for invasive blood pressure measurements is disclosed in German Patent No. 3,207,044 A1.
This transducer also is designed as a disposable device that comprises an integrated stop valve for drawing blood to be analyzed. In addition, this pressure transducer comprises an integrated capillary system for carrying out a rapid rinsing process.
Different types of disposable pressure transducers are described in the journal Health Devices of September, 1983, pp. 268-290, in an article entitled "Disposable Pressure Transducers." In some of these pressure transducers, certain electronic components and balancing resistors are accommodated in the reusable cable.
European Patent No. 0,124,308-B1 discloses a similar pressure transducer in which the pressure measuring element is inserted into an electrically insulated body in the form of a capsule and arranged such that it faces the chamber that contains the fluid to be measured. In this case, the electric conductor extends through the electrically insulated body and ends in connecting means inside of the housing so as to produce a connection for electronic circuitry.
European Patent No. 0,129,779 B1 discloses a similar pressure transducer with a plug/socket connection for connecting a reusable electric cable as well as a balancing card that is arranged in the cable and serves for balancing the resistors of the pressure transducer.
U.S. Pat. No. 4,603,574 discloses a pressure transducer in which a test resistor is arranged parallel to one branch of the Wheatstone bridge circuit in order to test the pressure transducer. The test resistor is connected in parallel to this branch in order to obtain a defined display value by simultaneously actuating two electronic switches. These two switches may be accommodated on the pressure transducer itself or in the supply cable.
German Patent No. 3,631,659 A1 discloses a pressure transducer for general purposes with a pin/socket connection for connecting the electric cable. The same also applies to German Utility Model No. 8,601,071.
European Patent No. 0,366,651 B1 discloses a pressure transducer with a short, rigidly soldered cable that is discarded together with the pressure transducer after use. This cable has a plug-in connection in order to be connected to an additional cable, whereby said additional cable is reusable and contains an electronic switch and a shunt resistor that is switched in parallel to one branch of the bridge circuit when depressing the switch so as to generate a defined display value.
The journal Health Devices of March, 1988, Vol. 17, No. 3, pp. 75-94 discloses additional disposable pressure transducers with one common characteristic, namely that a short cable that may be connected to a cable leading to the monitor via a plug-in connection is rigidly arranged on the pressure transducer.
German Utility Model No. 8,908,951 discloses a pressure sensor with an integrated plug housing.
The invention is based on the objective of improving the pressure transducer of the initially mentioned type in such a way that it has a simple and compact design, may be mounted in simple and inexpensive fashion, comprises only a few disposable parts, provides for simple and safe handling and, in particular, comprises a simple and safe electric connection to the cable leading to the monitor or another display device.
According to the invention, this objective is attained by the characteristics disclosed in claim 1. Advantageous embodiments and developments of the invention are disclosed in the subclaims.
Briefly stated, the disposable part of the pressure transducer according to the invention comprises only one housing and one substrate that is equipped with electric circuits and a pressure measuring element. The electric cable is connected by means of a special plug-in connector which directly contacts the contact surfaces of the substrate, i.e., without additional intermediate cable sections, overlapping the substrate and one housing cover in the fashion of pliers, and consequently produces the contact while largely relieving the substrate of mechanical loading.
The substrate according to one embodiment of the invention is simply placed into the housing and is retained therein by means of a preferably detachable cover.
According to an additional embodiment of the invention, the cover has an opening for one tongue of the plug-in connector. Consequently, the plug-in connector encompasses the substrate and the cover in the fashion of pliers. Since the entire surface of the cover adjoins the substrate, all mechanical forces generated by the plug-in connector also are absorbed by it.
The first chamber that contains the pressure measuring element is limited by one section of the substrate and insulated in a fluid-proof fashion via an annular seal that presses against the substrate. One additional annular seal is arranged on the cover such that it is situated essentially congruent to the aforementioned annular seal, whereby said additional annular seal presses against the side of the substrate situated opposite to the first chamber and consequently seals an opening that extends through the substrate and serves for balancing or calibrating the pressure transducer.
The fluid connections and a rinsing system are integrated into the housing of the pressure transducer such that they form a single component. In addition, a test key is integrated into the housing, whereby said test key is retained and guided in an opening of the housing, comprising at least one switching contact surface on its side that faces the substrate and cooperating with the switching contact surfaces that are printed on the substrate so as to test the system. This key consists of an elastic material, whereby the switching contact surfaces are arranged in such a way that no contact with the switching contact surfaces arranged on the substrate is produced if the key is not actuated due to the resilience of the elastic material. Consequently, no separate spring for the key is required as is the case with pressure transducers of the state of the art.
According to an additional embodiment of the invention, the pressure transducer and the plug-in connector may be fixed onto a holding plate that aligns the two aforementioned components in the correct position to one another and allows their coupling.